1. Field of the Invention
The invention relates to a (data) network having a number of routers, arranged in network nodes, for switching data packets. The invention further relates to a router and to a method for configuring a network, as well as to a method for aggregation and relaying of data packets, which are supplied to a router via a number of datastreams, to an output of the router.
So-called routers (data packet switching devices) are used for switching data packets in packet-switching networks. A router evaluates the addressing information contained in a data packet, and uses routing tables to determine the best onward route for the data packet through the network.
One serious problem in packet switching technology is the different propagation or delay times (delays) for packets in a datastream between a fixed transmitter and a fixed receiver. These different delay times are caused by different processing times in the individual network nodes (for example routers), and by the selection of different routes in the network. Fluctuations in the delay times are referred to as jitter. Both effects (delay and jitter) are particularly problematic in large networks and in time-critical applications.
The term “worst case delay” refers to the longest possible propagation time or maximum delay time which can occur in a network. This is an important parameter since receiving devices which receive data via the network are oriented to it. Normally, the maximum delay time in the network behaves in accordance with the relationship nh, wherein n denotes the number of datastreams which are supplied to that router for which the maximum delay time is observed, and h denotes the number of routers which are located upstream of this router in the network, in terms of the routing of a data packet.
In order to reduce delay times and jitter during packet transmission in a network, the IETF (Internet Engineering Task Force) proposes, in the differentiated service standard, that data packets from different datastreams which are received at a router be combined into one output stream at the output from the router, provided they have specific, matching classification features (“code points”). This aggregated output datastream is then dealt with and switched with priority in the router (so-called “expedited forwarding (EF) behavior”). This form of data switching can potentially be used for real-time services such as video or voice.
Data aggregation in a router requires that the data rate of the transmitted, aggregated datastream be matched to the data rates of the incoming datastreams from which the aggregated datastream is formed. A router admittedly has buffer-storage areas in which the data can be temporarily buffer-stored when the data traffic is excessive. However, in the longer term, the data rate of the transmitted, aggregated datastream must correspond at least to the sum of the data rates of the associated input datastreams since, otherwise, the buffer-storage facilities in the router would otherwise undoubtedly be swamped at some point in time, leading to loss of data.
Furthermore, the occurrence of so-called bursts (groups of data) in the input datastreams must be taken into account, representing a number of additional data bits which occur once and must be coped with by the router. For this reason, the rate of the aggregated, transmitted output datastream is in practice always chosen to be greater than the sum of the data rates of the input datastreams which form the output stream.
On the other hand, however, a high output datastream data rate from a router is not necessarily always advantageous since this, in turn, has to be coped with by a downstream router. It is thus already known for a minimum time separation to be specified for data packets in an aggregated output datastream, which must be complied with during transmission of such data packets (so-called “peak rate” limiting), which simplifies the task of a downstream router in the data line route.